What Do We Mean When We Say The Universe is Curved?

We know that NASA claims the Universe is flat, but it also said it's curved. What the what? How is that even possible? In this, the recently published second installment in an ongoing three-part series, Zogg the alien from Betelgeuse continues his journey of the Universe and its topology. Somewhat, Like the first episode, it's a truly amzing lucid introduction to the Cosmos, one in a really spetacular series of explainers on everything vision to sex, all from the perspective of a creature from beyond our solar system. Really top notch stuff.